This invention relates generally to electrophotographic image forming apparatus, and more particularly to cleaning devices for removing residual toner and debris from a charge retentive surface of an image-forming device.
In electrophotographic applications such as xerography, a charge retentive surface of a photoreceptor is electrostatically charged, and exposed to a light pattern of an original image to be reproduced, to selectively discharge the photoreceptive surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided, electrostatically attractable powder referred to as toner. Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original bean reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. The process is well known, and is useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly.
Multi-pass and single-pass color electrophotographic printing is substantially identical to the foregoing process of black and white printing. However, rather than forming a single latent image on the photoreceptor, successive latent images corresponding to different colors are recorded thereon. Each single color electrostatic latent image is developed with toner of a color complimentary thereto. This process is repeated in a plurality of cycles for differently colored images and their respective complimentary colored toner. Each single color toner image is transferred to the copy sheet in superimposed registration with the prior toner image. This creates a multilayered toner image on the copy sheet. Thereafter, the multilayered toner image is permanently affixed to the copy sheet as described above to create a color copy. The developer material (toner) may be a liquid material or powder material.
Although a preponderance of the toner forming the image is transferred to the paper during transfer, some toner invariably remains on the charge retentive surface of the photoreceptor, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, toner additives, kaolins and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimal imaging that the toner and debris remaining on the surface be cleaned thoroughly therefrom.
The quality of images produced by such equipment depends significantly on the ability to clean the photoconductive surface before it is reused.
Blade cleaning is a highly desirable method for removal of residual toner and debris (hereinafter, collectively referred to as "toner") from a photoreceptor. In a typical application, a relatively thin elastomeric blade member is provided and supported adjacent to and transversely across the photoreceptor surface with a blade edge chiseling (doctor mode) or wiping (wiper mode) toner from the surface. Subsequent to release of toner from the surface, the released toner accumulating adjacent to the blade is transported away from the blade area by a toner transport arrangement, or by gravity.
However, the blades are subject to wear and thus must be replaced. The need for replacement is unpredictable and usually requires a customer service engineer.
Accordingly, to simplify blade replacement and minimize service costs, a need exists for a multiple blade apparatus for cleaning residual toner and debris from the moving, charge retentive surface of an image forming apparatus, such that the blade holder of the multiple cleaning blade indexing apparatus is capable of positioning, loading and aligning each blade within allowable tolerances (as known in the art, tolerances are determined separately for applicable electrophotographic apparatuses). That is, the blade angle to the photoreceptor, blade load against the photoreceptor and alignment of the blade edge to the photoreceptor must be within operational tolerance zones. Further, the blade angle and blade load requirements demand that the blade be locked into position after indexing, and the blade edge alignment requirement dictates that the blade must be free to pivot and align itself to the photoreceptor plane with no interference from the indexing mechanism.
A number of cleaning apparatuses for photoreceptors, which employ a cleaning blade are known and may be briefly summarized as follows:
U.S. Pat. No. 5,394,228 to Godlove discloses a compact multi-blade cleaning system for a photoreceptor device. The blades are formed from a block of thermoplastic material, which has a plurality of parallel cuts extending partially therethrough. The uncut portion of the block forms a connecting member for connecting the plurality of cleaning blades at their securing edges. A mechanism advances the plurality of cleaning blades, one by one, into contact with the photoreceptor device.
U.S. Pat. No. 5,264,904 to Audi et al. discloses an apparatus which cleans a moving imaging surface with a cleaning blade and automatically detects a failure of the cleaning blade. A failure sensing mechanism detects the cleaning blade failure and activates a blade indexing mechanism. The indexing mechanism removes the failed cleaning blade and positions a new cleaning blade in a wiping or doctoring mode frictional contact with the imaging surface for cleaning.
U.S. Pat. No. 5,241,351 to Owens discloses a multi-blade holding apparatus that rotates from one blade to the next. The multi-blade holder holds the cleaning blades in place by using clamping inserts. The clamping inserts also allow for alignment and adjustment of the blades according to thickness. Spring-loaded pins secure the clamping insert to the core of the multi-blade turret holder.
U.S. Pat. No. 5,208,639 to Thayer et al. discloses a multiple turret style blade holder located such that an individual blade is selectively indexed into optimum position for cleaning residual toner and debris from a moving charge retentive surface. The blade holder contains a number of cleaning blades mounted radially from a central core. The indexing device removes the failed cleaning blade and positions a new cleaning blade in frictional contact with the photoreceptor for cleaning.
U.S. Pat. No. 5,081,505 to Ziegelmuller et al. discloses a rotatable wiper blade roller for cleaning residual toner particles from an image bearing surface and includes a plurality of indexable wiper blades. The blades engage the image bearing surface at an angle of 60.degree. to 85.degree. defined in the direction of particle removal by the cleaning edge of each such blade and image-bearing surface. The blades are cleaned secondarily by an intermittently rotatable brush that is completely out of contact with the image-bearing surface.
U.S. Pat. No. 4,451,139 to Yanagawa et al. discloses a cleaning apparatus for a photoreceptor, which includes an elastic polyurethane cleaning blade located downstream of a rotating brush with respect to the rotation direction of the photoreceptor.
U.S. Pat. No. 4,364,660 to Oda discloses a photoreceptor cleaning system having a cleaning blade, which removes toner from a photoreceptor. A brush located upstream of the cleaning blade acts as a toner recovery mechanism to recover toner removed from the photoreceptor by the cleaning blade.
U.S. Pat. No. 3,947,108 to Thettu et al. discloses a photoreceptor cleaning system wherein a blade acts as a primary cleaning member. A brush located downstream from the blade removes the residual film from the photoreceptor not removed by the blade.